Not Applicable
Not Applicable
The present invention is directed generally to optical transmission systems. More particularly, the invention relates to optical transmission systems including protection capability for use it optical communication systems.
Communications transport systems are used to transport information over a substantial portion of the world. This extensive communication access requires enormous amounts of equipment to provide the necessary infrastructure for the systems. In addition, much of the equipment and almost all of the transport media is remotely located and necessarily exposed to the environment.
It view of the necessary exposure of transmission systems to uncontrolled environments, it is not uncommon for failures to occur in links along a transmission path. However, it communication systems are to be effective, it is necessary to have a high degree of reliability in the system. Thus, communication systems must provide for protection of the information being transmitted through the systems, as well as for restoration of failed links in the system.
The reliability of service provided by a transmission system is inversely proportional to the frequency of failures in the transmission system. One of the most common failures in fiber optic transmission systems is a fiber break. When a fiber break or other failure occurs in a transmission link, the traffic intended to pass through the link must be rerouted through another path until the link is restored.
Another common source of failures in optical transmission systems is an equipment failure. The amount of traffic that is lost upon an equipment failure depends upon the particular piece of failed equipment in the system. For example, in most, if not all, currently available fiber optic transport systems, a line amplifier failure will result in a complete loss of traffic traveling through an optical link containing the failed line amplifier. Whereas, a transmitter or a receiver failure will generally result only in the loss of the wavelengths associated with the failed transmitter or receiver. When an amplifier fails or fiber cut occurs, traffic must be rerouted through a new path. When a transmitter or receiver fails, the traffic must be transferred to a different transmitter and/or receiver using the same or a different channel and/or transmission path.
Despite the persistent hazards of uncontrolled exposure to environmental conditions and inevitable equipment failures, it is imperative that communications service providers supply high quality service. Therefore, service providers have developed protection schemes to provide automatic traffic restoration upon a transmission link failure and have required redundant equipment systems to decrease the effective failure rate of tie link.
Protection schemes are generally categorized based on whether it is a channel or a path being protected. In channel protection schemes, if information is transmitted on both a working channel and a protection channel, the schemes are referred to as providing one plus one (xe2x80x9c1+1xe2x80x9d) protection. Conversely, if information is switched from a working channel to protection channel or working path to a protection path only when a failure occurs, the schemes are referred to as one for one (xe2x80x9c1:1xe2x80x9d) protection schemes. More generally, M protection channels or paths can be shared between N working channels or paths, which is generally designated as M:N protection. Similarly, M protection channels can carry the same information as the working channel to provide 1+M protection.
In xe2x80x9c1+1xe2x80x9d schemes, the information is sent along to two different paths from an origin node to a destination node. At the destination node, one of the two signals is used and the other is discarded. Normally, the working channel is used and the protection channel is discarded, but when a failure in the working channel transmission occurs, the protection channel is used. In xe2x80x9c1:1xe2x80x9d schemes, either the working channel is switched to a protection path or the information is switched to a protection channel on the protection path.
Channel protection schemes can be implemented along with various multiple fiber path protection schemes. Path protection can be performed if at least one redundant path is available between the origin and destination nodes. For a path to be fully protected, there must not be any common links in the redundant paths.
While there is no inherent requirement that the same fiber route be used to transmit information in both directions (East-West and West-East, etc.), many system topologies are configured employing this requirement and protected as rings. Ring configurations and protection schemes are based on using the same fiber route for either the working or protection traffic in each direction between two nodes, which allows the information being transmitted to be fully contained within the ring. Most path protection schemes are generally analogous to two classes of ring protection schemes, except the same fiber route limitation may not be imposed. The first class of protection schemes is referred to as Bi-directional Line-Switched Ring (xe2x80x9cBLSRxe2x80x9d) in SONET, or Multiplex section-Shared Protection Ring (xe2x80x9cMS-SPRingxe2x80x9d) in SDH. The second class is known as Unidirectional Path-Switched Ring (xe2x80x9cUPSRxe2x80x9d) in SONET, or Dedicated Protection Ring (xe2x80x9cDPRingxe2x80x9d) in SDH. BLSR and UPSR schemes can be implemented using two or more fibers interconnecting nodes, which either electrically or optically switch traffic between the working and protection paths established by fiber rings.
In BLSR schemes, working channels for each direction connection two nodes are transmitted on different rings in the same working path. Protection for the working channels is provided using one or more different rings in a common protection path. In UPSR schemes, different working paths for each direction are provided on the same ring and the protection paths are provided on other rings. The protection path in one direction is common with the working path in the other direction.
In the event of a failure of the working path, a destination node for the traffic will switch to the protection path to receive the traffic in both 1+1 and 1:1 schemes. In 1:1 schemes, an origin node for the traffic and/or other nodes between the origin and destination node will also switch the traffic to the protection path to route traffic around the failure.
As the demand for transmission capacity continues to grow, there is an increasing need to efficiently use the available transmission capacity and protect the information being transported through the systems. However, some systems do not, or will not, have sufficient fiber or capacity to provide traditional multiple fiber protection schemes.
In addition, the increased amount of traffic being carried on each fiber places increased importance on the ability to effectively protect the information, because each failure results in higher revenue losses for service providers. Accordingly, there is a need for optical transmission systems and protection schemes that provide effective protection with increasing wavelength efficiencies for use in long distance communication systems.
The present invention addresses the need for higher reliability optical transmission systems, apparatuses, and methods. Optical systems of the present invention include at least one optical amplifier configured to provide partitioned amplification, or gain, over the range of signal wavelengths carrying information between optical signal processing nodes. The optical amplifier is configured to partition the gain provided to a plurality of wavelength groups such that the gain imparted to a wavelength group is only partly interdependent on, or independent of, the gain imparted to other wavelength groups.
The optical system can thus be configured to transmit information using working wavelengths, or channels, and one or more corresponding protection wavelengths, or channels, in different wavelength groups in the same fiber. The information can be transmitted simultaneously to provide a single fiber 1+N type protection. Similarly, the information can be switched from the first wavelength to the second wavelength upon a failure to provide single fiber M:N type protection. This protection scheme can be used in both uni- and bi-directional optical transmission systems to provide single fiber protection in the event of various transmitter, receiver, and amplifier failures.
The optical amplifiers generally include amplifying media and power supplies that provide gain in different wavelength groups to produce optical amplifier gain partitioning. Therefore, if an amplifier power supply fails for one wavelength group, the remaining amplifier power supplies continue to function and provide optical amplification for the remaining, or surviving, wavelength groups.
The optical amplifiers can include a single stage or multiple stages that provide independent or partly interdependent gain to the wavelength groups. For example, various embodiments include distributed and/or concentrated Raman amplifiers employing a plurality of pump wavelengths configured to provide partitioned gain in one or more serial amplifier stages. The different Raman stages can provide gain for some or all of the wavelength groups in similar or varying gain profiles and amplification levels. Similarly, doped fiber amplifiers providing partitioned gain can be used in one or more stages alone or in combination with Raman fiber amplifiers. The optical amplifier stages can also include stages having the same or different optical amplifier designs.
The protection scheme of the present invention increases the reliability of both uni-directional and bi-directional optical systems by reducing the number of line amplifier failure scenarios resulting in an optical link failure that requires the rerouting of traffic. This reduction in the number of optical link failures is particularly beneficial in optical fiber transmission systems that do not provide multiple independent paths between nodes. In those systems, the present invention provides protection for traffic being transmitted either uni- or bi-directionally on a single fiber, in addition to any protection that may be available using multiple fiber protection schemes it the same or different paths.
Accordingly, the present invention addresses the aforementioned concerns by providing optical systems apparatuses, and methods having increased reliability. These advantages and others will become apparent from the following detailed description.